ESTIMATING SENSIBLE AND LATENT-HEAT FLUXES FROM A TEMPERATE BROAD-LEAVED FOREST USING THE SIMPLE BIOSPHERE (SIB) MODEL

Sensible (H) and latent heat (lambda E) flux densities from a well-wat ered, broad-leaved forest of Nothofagus trees were estimated using the simple biosphere (SiB) model. Model inputs included micrometeorologic al measurements made at a reference height (36m) just above the canopy and site parameters such as the tree canopy leaf area index of seven. Half-hourly diurnal courses of modelled H and lambda E were generally in good agreement with eddy covariance flux measurements (+/- 30Wm(-2 ) on average) over six late-summer days of variable weather conditions . The most important model variables determining these fluxes were the bulk leaf boundary-layer resistance (r(b)), proportional to leaf size , for H and canopy (stomatal) resistance (r(c)), regulated by radiatio n interception and air saturation deficit, for lambda E. Recent develo pments in the modelling of r(c) for different vegetation types are dis cussed. Maximum daily ground (forest floor) evaporation rate (E-g) was 0.5 mmday(-1), accounting for up to 20% of forest evaporation. Initia l model estimates of E-g in the forest were nearly 50% less than those of lysimeter measurements. However, agreement between measured and mo delled E-g was only about +/- 0.05 mm day(-1) after reduction of the t runk space eddy diffusive resistance (r(d)) based on a comparison with other values in the literature. (C) 1997 Elsevier Science B.V.